Set Specific Bit in Byte Array

arrays, bit-shift, c#

Solution

The process of selecting a specific bit consists of two steps:

- Picking the byte, and then

- Picking the bit.

Picking the byte is simple: all you need to do is dividing the bit index by the number of bits in a byte - i.e. dividing by eight:

int byteIndex = bitIndex / 8;

Now that you know what byte to use, calculate which bit you want to access. For that you need to compute a remainder of a division by eight, like this:

int bitInByteIndex = bitIndex % 8;

With these two indexes in hand, it is easy to access the bit: use `1 << bitInByteIndex` as a mask, like this:

byte mask = (byte)(1 << bitInByteIndex);
bool isSet = (bytes[byteIndex] & mask) != 0;
// set to 1
bytes[byteIndex] |= mask;
// Set to zero
bytes[byteIndex] &= ~mask;
// Toggle
bytes[byteIndex] ^= mask;

Problem

Original source

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